- Records reveal 2,644 adults were caught lying to enter the UK from 2010 to 2016
- Only 580 of those are kicked out after being caught posing as a vulnerable child
- Two-thirds of 692 claimants whose aged was challenged in 2017 were over 18
- Officials do not carry out medical tests, subjecting them instead to rigorous interviews
Only one in five lone child migrants caught lying about their age in a bid to stay in the UK is deported, damning figures have revealed.
More than 2,500 of the 13,600 unaccompanied child asylum seekers who have come to Britain since 2010 have been found to be over 18. But fewer than 600 have been returned home.
The statistics expose the extent to which some adult migrants are trying to deceive the authorities.
More than 2,500 of the 13,600 unaccompanied child asylum seekers who have come to Britain since 2010 have been found to be over 18
Experts warned that the small chance of being deported even when they are caught lying was helping to fuel the influx of migrants across the Channel.
The figures emerged as the Daily Mail found that councils are paying £305 million a year to look after child migrants who come to the country without parents or carers.
The number of unaccompanied asylum seeking children (UASCs) cared for by councils has more than doubled in four years – rising from 1,950 in 2013 to at least 4,560 at the end of March.
Council chiefs say they are struggling to cope – accusing the Government of funding only about half of the £67,600 needed annually to care for each of them.
Figures obtained using Freedom of Information laws showed that 13,641 applications for sanctuary from lone child migrants were made between 2010 and 2016.
Home Office data revealed that 2,644 were actually found to be over 18 when their age was disputed – but only 580 were either removed forcibly or voluntarily went home, a rate of 21.9 per cent.
Latest available figures show that in the year to September, 457 of the 695 so-called 'child' migrants challenged by officials actually turned out to be adults.
A row flared in October 2016 amid mounting concern that adult refugees were lying about their ages to gain entry to Britain.
Calls for the Home Office to carry out dental checks grew after suspiciously mature-looking child migrants were among those who arrived from the 'Jungle' shanty-town in Calais to be reunited with relatives as part of a resettlement programme.
The statistics expose the extent to which some adult migrants are trying to deceive the authorities. Experts warned that the small chance of being deported even when they are caught lying was helping to fuel the influx of migrants across the Channel
A clamour for tooth tests erupted after doubts surfaced over the ages of some of the 38 refugees arriving in the UK from the squalid migrant camp in northern France.
Officials insisted all the migrants were aged under 18. But some looked several years older – with crow's feet and flecks of grey hair.
Tory MP David Davies said: 'These figures are not giving the whole picture.
'In many cases where age is disputed the individual is given the benefit of the doubt.
'But they do point to an increasing problem of wholesale abuse of the asylum system by people who simply want to come here because they know they will be treated sympathetically when they arrive.'
Tony Smith, former director-general of UK Border Force, said: 'This is a good indicator of illegal entry into the UK.
'While it is important to afford protection in the UK to vulnerable children, we cannot ignore the fact that more than half of them [challenged by officials] are found to be over age after a thorough assessment. Even then, only a small number are sent back.'
If individuals are caught trying to cheat the system, there is nothing to stop them applying for asylum as an adult once they are in Britain.
If children claim asylum in the UK they become the legal responsibility of the local council in whose area they are discovered.
One in 16 children being looked after by town halls are now unaccompanied asylum seekers, compared with one in 33 in 2013.
Council chiefs say the arrivals have significant implications for the taxpayer because councils are responsible for all costs associated with child asylum seekers until they are 25. This includes schooling, foster care or children's homes, through to university fees and housing costs.
Local authorities say the shortfall in government funding could lead to cuts in services – or rises in council tax.
A survey by the Mail has found that almost every council in the country is caring for UASCs.
Town halls with the greatest number are in Croydon in south London, Kent or in areas crossed by major roads, where children escape from the back of lorries at service stations.
Shropshire Council was left with a £1 million bill after ten 'highly vulnerable' Vietnamese children were abandoned.
The girls and boys aged 13 to 16 travelled to the UK from France in the back of a lorry.
Peter Nutting, leader of the Tory-run council, said the unforeseen situation was one of the reasons it needed to save an extra £5 million by the end of this financial year.
In October, nine boys from Eritrea were found in the back of a lorry at a motorway service station in Surrey.
They were taken into the care of Surrey County Council but it said it was struggling to cope financially because it was already paying for 130 UASCs.
Staffordshire County Council, which is looking after 135 lone child migrants, said it faced a shortfall of £100,000 by March.
Lincolnshire County Council, which cares for 46 UASCs, spent £1.63 million in 2016-17 but received only £1.28 million from the Home Office.
Hertfordshire County Council has 95, including children from Eritrea, Vietnam and Somalia. In 2016-17, the council spent £3.3 million but received only £2.1million from the Government.
David Simmonds, of the Local Government Association, said: 'No one is disputing these children need to be cared for. We have a good track record when it comes to looking after them.
'The UK does a good job by these young people, take them in, find them accommodation... they do quite well, they go on to university... but councils quite simply cannot afford it.
'It could lead to services being cut back elsewhere.'
Many young asylum seekers go missing soon after they have been placed into care, amid fears they fall easily back into the hands of gang masters and traffickers.
A Home Office spokesman said: 'We take our responsibility in asylum cases involving children very seriously and we are very clear that we will not tolerate abuse of the system, especially from adults claiming to be children.
'Where there is no documentary evidence to prove an asylum seeker's age, but their claimed age is disputed, the Home Office will refer them to social services for an age assessment.'